The present invention relates to control systems for boiler burner apparatus and more specifically to a control system which is adaptable for controlling any one of a plurality of burner systems in accordance with a specification unique to the particular system.
The design approach to burner control systems currently manufactured is to develop a logic scheme in accordance with a specification provided by a customer, usually a utility company, in need of a control system for assuring the safe and reliable operation of the boiler installation. Many of the specifications are standardized in terms of the safety requirements and certain operating sequences. However, there are enough variations from one boiler installation to another to require, for all practical purposes, a custom design for each control system put into service.
The design engineer, responsible for the fabrication of the system, typically must convert the specification into a series of logic sequences and thereafter convert the logic sequences into a series of interrelated circuits utilizing functional logic devices to effect the final design. In addition, the typical system requires a considerable amount of documentation in keeping with engineering practice. For a typical twelve burner system, the engineering and documentation requirements become very costly, which costs seem unwarranted and unjustified in terms of the repetitiveness and tedium associated with such designs.
Control systems of the type mentioned above, in addition to requiring a great deal of design time, also require an inordinate fabrication time, since a major portion thereof must be handwired using color-coded wiring harnesses and hand soldering for most of the connections. Each of these connections must thereafter be checked not only during the manufacturing stage but also in numerous test runs, in order to assure that the burner control system operates in the manner intended, is reliable, and very importantly meets the safety requirements which are critical.
In order to conserve space and reduce the manufacturing time, many control systems now utilize solid state printed circuit boards, grouped together in a housing, having drawers or bays therein, each bay associated with one burner. Disposed within the bays, there is typically a rack of connectors into which the printed circuit boards are inserted. In such a system, there may be as many as a hundred printed circuit boards for each burner with a multiplicity of cross-connections between cards and connections to other devices.
Feedback signals provide indications as to the status of externally operated devices and these signals are communicated to the different portions of the control system to affect the complex control of the burner system under consideration.
In the present invention, the control system or sub-system, as a whole, is not thought of as one overall unit; but, rather, as a multiple number of sub-units, each having absolute responsibility over its particular function.
This is a departure from past industry applications of digital logic control systems, wherein the overall control system or sub-system has been comprised of a multiple number of cards which, in themselves, did not have absolute control of a piece of hardward, i.e., control of equipment, such as an Ignitor Lighting Sequence, may have encompassed logic gates that were spread over several cards, and intermixed on these cards with logic gates associated with control of other equipment.
A logical functional card on the other hand takes all of this intermixed or distributed logic and lumps it on one card which then has a designated purpose or function. In addition, logic has been placed on the logical functional card to provide it with flexibility enough to handle any logic sequence associated with the designated purpose or function of that respective card which may vary from one burner system specification to another.
By selective interconnection of various designated logical function cards, one ends up with a completely customized system that will control the overall system or sub-system as a whole.
The concept of the present invention is designed to dramatically reduce the engineering time required to convert the specification into a set of circuit diagrams and the associated documentation thereof. Further, it is clear that fabrication time is substantially reduced since the concept eliminates a great deal of cross-wiring from one card to another.
Each of the great majority of burner control systems generally in use, requires certain functions to be performed in a certain sequence. The sequence may vary from one burner system to another but certain functions seem to be generally required. One such function almost universally required in burner control systems is the purging of the boiler of combustible mixtures of gases before a lightoff of the boiler may be effected. Such purging, for example, requires opening of air vents and the start-up of large fans or blowers which draw fresh air into and through the boiler. The purge sequence can be specified as a sub-system with one function or one logical function of a typical burner control system. Another logical function might be the prelight sequences which check for certain conditions, one of which being the completion of the previously mentioned purge sequence as well as other safety conditions which must be satisfied previous to the initiation of the prelight sequence.
The system concept of the present invention rearranges the manner in which the design approach to a custom boiler control system is effected by taking into account certain universally required functions and thereafter, modifying the arrangement of certain ones of these functions for the specific application involved. If the common matter is lumped into standard logical function cards including extra circulatory for peculiarities of the various systems, then a system can be adapted for any burner control system of the general type now in use and only reference to the specification may be made to customize the system to the particular boiler in question.
It is therefore an object of the present invention to provide a system for controlling a boiler burner system which is adaptable to most boiler systems now in use.
It is another object of the present invention to simplify the arrangement of components of a boiler control system so that engineering and fabrication requirements are greatly reduced.
It is another object of the present invention to adapt a burner control system from a functional logic arrangement to a logical function arrangement.